JP3535017B2 - Polarization rotating device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed polarization rotation device applicable to manufacturing development / selection of devices used for optical communication, optical switching, optical information processing and the like.

[0002]

2. Description of the Related Art Considering the construction of an optical transmission processing system using light such as optical communication, optical switching, and optical information processing, the polarization dependence of each device becomes a serious problem. For example, when a semiconductor laser type optical amplification element as shown in FIG. 8 is used to compensate an optical loss in an optical fiber or an optical switch, the gain characteristic varies depending on the polarization state of the input signal light. If this happens, the light-receiving level on the light-receiving side fluctuates with time, and the reception sensitivity is greatly reduced.

Therefore, each device is required to have a performance such as a polarization dependence of 0.5 dB or less, and it is necessary to measure the polarization dependence. At this time, it is necessary to perform the measurement before mounting the optical fiber on a device such as a semiconductor laser type optical amplifying device to form a module, that is, in a chip state.

By the way, the active layer of the optical amplifying element has a size of, for example, a width of about 0.4 μm and a thickness of about 0.4 μm, as shown in FIG. The device is adjusted to the optimum position, and the optical signal is input in that state for measurement. The same applies to the fiber on the output side.

The tolerance of the optimum alignment device in the direction perpendicular to the optical axis is very strict, and the coupling loss is 1 dB down tolerance, which is only about 0.5 micron. The fine alignment device can adjust the position in units of 0.1 micron,
For example, it is extremely difficult to keep the optimum state for several tens of seconds or longer.

In order to measure the polarization dependence, the polarization of the input light is rotated and the gain at that time is measured. For this reason, conventionally, the polarization dependence is measured using a polarization controller in which a half-wave plate and a quarter-wave plate are combined.

FIG. 9 is a diagram for explaining measurement using a conventional polarization controller. In FIG. 9, 1100
Is a light source, 1101 is a polarization controller for rotating the polarization direction of light, 1102 is a quarter-wave plate, 1103 is 1/2
Wave plates, 1104, 1105 are spherical fibers, 1106
Is a semiconductor laser type optical amplification element to be measured, and 1107 is a light receiving element. Here, the wave plate 11 is used to rotate the plane of polarization.
It is realized by mechanically rotating 02, 1103.

[0008]

Conventionally, the half-wave plate 1 has been used.
The polarization dependence was measured by using the polarization controller in which the 102 and the quarter wave plate 1103 are combined.
It took about 30 seconds to obtain all polarization states. However, as mentioned above, it is difficult to keep the spherical fiber in the optimum state for several tens of seconds or more, and the measurement accuracy decreases due to the axis deviation while rotating the polarization plane, and the polarization dependence of 1 dB or less must be measured. Was impossible. Therefore, there has been a demand for a polarization rotation device capable of rotating the polarization plane at a high speed and ending the measurement before the alignment axis is displaced.

Therefore, an object of the present invention is to provide a polarization rotation device capable of high speed processing.

[0010]

In order to solve such an object, the invention of claim 1 provides a transmitting / reflecting means for transmitting and reflecting a part of light and a total reflection means for totally reflecting the light. And a rotating means that is installed between the transmitting / reflecting means and the total reflecting means and rotates the polarization direction of light by n degrees (0 <n <360). Single
Input the light of the light, the light transmitted through the transmission / reflection means is looped between the transmission / reflection means and the total reflection means.
By reciprocating a plurality of times with, by rotating the polarization direction of light by a predetermined angle minutes, more which the polarization direction is rotated
The pulsed light is output from the transmitting / reflecting means.

According to a second aspect of the present invention, in the polarization rotation device according to the first aspect, further comprising a separating means for separating the light input to the transmission / reflection means and the light output from the transmission / reflection means. It is characterized by that.

According to a third aspect of the present invention, in the polarization rotating device according to the first or second aspect, an amplifying means for amplifying light is provided between the transmitting / reflecting means and the total reflection means. Is characterized by.

According to a fourth aspect of the present invention, first transmitting / reflecting means and second transmitting / reflecting means for transmitting and reflecting a part of light, the first transmitting / reflecting means and the second means. A single-pulse light for the first transmitting / reflecting means, the rotating means being installed between the transmitting / reflecting means and rotating the polarization direction of the light by n degrees (0 <n <360). Input, and the light transmitted through the first transmitting / reflecting means is transmitted through the first transmitting / reflecting means.
A loop structure is provided between the reflecting means and the second transmissive reflecting means.
By reciprocating a plurality of times with, by rotating the polarization direction of light by a predetermined angle minutes, more which the polarization direction is rotated
The pulsed light is output from the second transmitting / reflecting means.

According to a fifth aspect of the present invention, in the polarization rotating device according to the fourth aspect, an amplifying means for amplifying light is installed between the first transmitting / reflecting means and the second transmitting / reflecting means. It is characterized by doing.

[0015]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

(Embodiment 1) FIG. 1 shows a sectional structure of a waveguide. In FIG. 1, 101 is an InP substrate, 102 is a waveguide layer, and InGa having a bandgap wavelength of 1.3 μm.
AsP (0.3 μm thick), 103 is I with a thickness of 1.5 μm
A ridge having a width of 1.5 μm is formed of nP. 10
Reference numeral 4 is guided light.

FIG. 2A shows the structure of a high speed polarization rotation device. In FIG. 2A, reference numerals 106 and 109 denote the waveguides shown in FIG. 1, and particularly reference numerals 107 and 108 denote loop structure portions. 110 is a coating that transmits 50% of the propagated light and reflects 50%, and 111 is a total reflection coating. 110 and 111 coatings are TiO ₂ / Si
It consists of O ₂ . Reference numeral 112 denotes a polarization rotator that rotates the linearly polarized light of the propagating light by 5 degrees. Reference numeral 114 denotes an input light, which inputs a single pulse as shown in FIG. A single pulse has a linear polarization.

The input single pulse is the coating 11
As shown in FIG.
In addition to obtaining all linear polarization states in 18 turns by rotating 0 degrees, a part 115 of the coating 110 is output.

The length of the reciprocating portion (resonance length) is about 0.5 cm.
Assuming that, the single pulse is output so as to rotate at 10 ps at 100 ps, so that all linear polarization states are obtained in a short time of about 2 ns. Therefore, in the measurement using this device and the oscilloscope, the polarization dependence can be obtained before the axis deviation occurs. Note that the optical pulse is attenuated more and more due to the transmission loss and the waveguide loss at 110 every time the optical pulse travels back and forth. Therefore, for example, when the pulse disappears after 18 rounds, a new single pulse 114 is input. As the polarization rotator, for example, the structure described in Japanese Patent Application No. 8-270527, "Asymmetric Arrangement Lattice Polarization Control Element" can be adopted.

(Embodiment 2) FIG. 3 shows the configuration of Embodiment 2 of the present invention. 3, the same parts as those of the first embodiment shown in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted. In the second embodiment, in addition to the first embodiment of FIG.
By having 9 optical circulators (or optical couplers), input light and output light are separated.

(Embodiment 3) FIG. 4A shows the configuration of Embodiment 3 of the present invention. In FIG. 4A, the same parts as those in Embodiment 1 of FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. The third embodiment of FIG. 4 has a semiconductor optical amplifier 215 in addition to the first embodiment of FIG. The semiconductor optical amplifier 215 is joined to the waveguide of FIG. 1 by a butt joint. With this semiconductor optical amplifier 21, the intensity of a part of the output light can be kept constant as shown in FIG.

FIG. 5 shows a sectional structure of the semiconductor optical amplifier 215. Here, 201 is an n-InP substrate, and 202 is an n-I.
The nP clad layer 203 has a thickness of 0.4 μm and a width of 0.4 μm.
m, a band gap wavelength of 1.5 μm, an InGaAsP active layer, 204 is a p-InP clad layer, 205,
206 is an Fe-InP insulating layer, 207 is p-InGaA
sP cap layer, 208 is an n-side electrode, and 209 is a p-side electrode. The total length is 300 μm.

With this (semiconductor) optical amplifier 215,
The transmission loss and the waveguide loss due to the coating 110 can be compensated, and the pulse attenuation can be prevented (FIG. 4).
(See (b)). When the length of the loop structure is about 0.5 cm, a single pulse is output so as to rotate at 10 ps at 100 ps, so that all linear polarization states can be obtained in a short time of about 2 ns. Therefore, in the measurement using this device and the oscilloscope, the polarization dependence can be obtained before the axis deviation occurs. Since noise is accumulated by the spontaneous emission light of the optical amplifier, for example, when the pulse disappears after 18 rounds, the optical amplifier is turned off to reset the spontaneous emission light once, and then a new single pulse 114 is input.

(Embodiment 4) As shown in FIG. 6, when the coating 111 is not a total reflection coating but a coating of 50% transmission and 50% reflection, the separation of input and output can be measured. Here, an extra (partial) output light is provided by providing an optical isolator on the input side that has a small loss for right-handed input light and a large loss for a part of output light 115 in the opposite direction. It is also possible to cut 115.

(Fifth Embodiment) Further, as shown in FIG. 7 in addition to the fourth embodiment of FIG. 6, a (semiconductor) optical amplifier 415 is provided to compensate for transmission loss and waveguide loss due to the coating 110. It is possible to prevent the pulse from being attenuated.

In the above embodiment, the n-type I
Although the nP substrate has been described as an example, the same effect can be obtained with a p-type substrate and other semiconductor crystals. Although an example of bulk InGaAsP is given as the active layer, a quantum well structure or a strained quantum well structure (compressive strain,
Stretch strain) may be used. Also, InGaAlAs
Similar effects can be obtained with material systems such as InAlAs, InAlAs, and AlGaAs.

Further, the core layer exists below the ridge with respect to the ridge shape, but a structure in which the core layer is etched halfway during the formation of the ridge shape does not change the gist of the present invention. It is also possible to use a buried waveguide structure.

Further, as an embedded structure of the optical amplifier, p
The current constriction due to the n-junction may be used. An optical fiber amplifier can also be used as the optical amplifier.

A quartz waveguide, an optical fiber, or a space system may be used as the waveguide.

Further, a mirror of 50% transmission / 50% reflection,
A grating may be used as the total reflection mirror instead of the multilayer coating.

[0031]

As described above, in the inventions of claims 1 and 4, the transmission / reflection means such as a coating and the total reflection means (two transmission / reflection means in the fourth embodiment) are provided. The light is reciprocated, and the polarization direction of the light is sequentially rotated by a rotating means such as a rotator. By outputting the light whose polarization direction is rotated from the transmission / reflection means, the polarization plane can be rotated at a higher speed than in the conventional case.

In the invention of claim 2, since the input light and the output light are separated by the separating means such as an optical circulator,
There is no mutual influence between the input light and the output light.

According to the third and fifth aspects of the present invention, it is possible to guarantee the attenuation during the round trip of the light by amplifying the light.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a waveguide according to a first embodiment of the present invention.

2A is a configuration diagram of a high-speed polarization rotation device of Embodiment 1 of the present invention, and FIG. 2B is a timing chart showing a polarization direction of light.

FIG. 3 is a configuration diagram showing a configuration of a high-speed polarization rotation device according to a second embodiment of the present invention.

4A is a configuration diagram of a high-speed polarization rotation device according to a third embodiment of the present invention, and FIG. 4B is a timing chart showing a polarization direction of light.

FIG. 5 is a sectional view showing a structure of a semiconductor optical amplifier.

FIG. 6 is a configuration diagram showing a configuration of a high-speed polarization rotation device according to Embodiment 4 of the present invention.

FIG. 7 is a configuration diagram showing a configuration of a high-speed polarization rotation device according to a fifth embodiment of the present invention.

FIG. 8 is a perspective view showing a structure of an optical amplification element.

FIG. 9 is a configuration diagram showing an example of a system using a conventional polarization controller.

[Explanation of symbols]

106, 109 Waveguide 107,108 Loop structure part 112 Polarization rotator 110,111 coating 114 input light 115 Partial output 215 (Semiconductor) optical amplifier

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 27/28 G02B 6/14 G02F 1/00-1/125 JISST file (JOIS)

Claims (5)

(57) [Claims] 1. A transmitting / reflecting means for transmitting and reflecting a part of light, a total reflection means for totally reflecting light, and a device provided between the transmitting / reflecting means and the total reflection means,
A rotating means for rotating the polarization direction of light by n degrees (0 <n <360), inputting a single pulse of light to the transmitting / reflecting means, and transmitting the light transmitted through the transmitting / reflecting means. The transparency
Using a loop structure between the reflection means and the total reflection means,
By reciprocating several times , the polarization direction of light can be changed by a predetermined angle.
Multiple pulses that are rotated in each
A polarization rotation device, characterized in that the light of (1) is output from the transmitting / reflecting means. 2. The polarization rotation device according to claim 1, further comprising a separating means for separating the light input to the transmitting / reflecting means and the light output from the transmitting / reflecting means. Polarization rotation device. 3. The polarization rotating device according to claim 1, wherein an amplifying means for amplifying light is provided between the transmitting / reflecting means and the total reflection means. Wave rotation device. 4. A first transmission / reflection means and a second transmission / reflection means for transmitting and reflecting a part of light, and a first transmission / reflection means and a second transmission / reflection means. It is installed in between and changes the polarization direction of light by n degrees (0 <n <36
0) rotating means for rotating, inputting a single pulse of light to the first transmitting / reflecting means, and transmitting the light transmitted through the first transmitting / reflecting means to the first transmitting / reflecting means. The polarization direction of the light is rotated by a predetermined angle by moving back and forth between the means and the second transmissive / reflecting means a plurality of times by using a loop structure. A polarization rotation device, wherein a plurality of pulsed light beams whose directions are rotated are output from the second transmission / reflection means. 5. The polarization rotation device according to claim 4, wherein the first transmission / reflection means and the second transmission / reflection means.
A polarization rotation device, wherein amplification means for amplifying light is installed between the reflection means.